Hydraulic brake fluids



United States Patent US. Cl. 252-73 2 Claims ABSTRACT OF THE DISCLOSURE A hydraulic brake fluid consisting essentially of a poly(oxyethylene-oxy-1,2-propylene) glycol monomethyl ether having an average molecular weight of from about 160 to about 230 and the formula.

wherein n averages from 1 to 3.7, m averages from 0.3 to 3 and the average total of n and m is from 3.1 to 3.9 and the oxyethylene groups constitute from 65 to 90% by weight of the total weight of oxyalkylene groups present.

This application is a continuation-in-part of Ser. No. 638,557, now abandoned.

The present invention relates to a novel hydraulic brake fluid and to the method of applying pressure to a hydraulic brake by the use of that fluid.

In these days of growing use of automotive vehicles of greater weight and horsepower and operation thereof at higher speeds and throughout the winter in areas having very cold winters, there is an ever greater need for hydraulic brake fluids which not only have a higher boiling point and a suitable viscosity at high temperatures as well as being low in rubber-swelling but which also have a relatively low viscosity at low temperatures and a low freezing point.

Conventional hydraulic brake fluid compositions have very high viscosity at low temperatures which results in poor brake operation at such temperatures. In order to overcome this defect, additional components, such as diethylene glycol monoethylether, ethylene glycol monobutylether and the like may be added to the hydraulic brake fluids as a viscosity depressant. However, if these are added in amounts suificient for lowering viscosity, the boiling point of the fluid is depressed to an undesirable degree.

Also in the prior art there has been proposed for use as hydraulic brake fluids polyoxyalkylene glycol monoalkyl ethers of high boiling point and somewhat lower than conventional viscosity at low temperatures. In this respect, reference may be made to US. Pat. Nos. 3,062,- 747 and 3,324,035.

According to the present invention, there are provided as hydraulic brake fluids polyoxyalkylene glycol monoalkyl ethers superior to those provided in the aforementioned two patents, particularly with respect to having low viscosity at very low temperatures, while at the same time meeting the other requirements for hydraulic brake fluids. More particularly, there is provided according to the invention a hydraulic brake fluid consisting essentially of a poly(oxyethylene-oxy-l,2-propylene) glycol monomethyl ether having an average molecular weight of from about 160 to about 230 and the formula 3,528,920 Patented Sept. 15, 1970 wherein n averages from 1 to 3.7, m averages from 0.3 to 3 and the average total of n and m is from 3.1 to 3.9 and the oxyethylene groups constitute from 65 to by weight of the total weight of oxyalkylene groups present.

The block character of the polymers represented by the above formula and the arrangement of the ethylene oxide and propylene oxide units in the molecule, also as represented in the above formula, are critical to the present invention. In this regard, in the preparation of the polyoxyalkylene glycol monomethyl ethers which serve as brake fluids according to the invention, a procedure is always followed such that this particular block copolymer structure will result. Thus, for example, in conventional processes for the preparation of polyoxyalkylene glycol monoalkyl ethers, the procedure to be followed for the preparation of the block copolymers according to the invention is initially to carry out the addition reaction of ethylene oxide with methanol to form a polyoxyethylene glycol monomethyl ether and then to carry out the addition reaction with that ether of propylene oxide. These reactions are ordinarily carried out in the presence of a catalytic amount of an alkaline catalyst, such as sodium hydroxide or potassium hydroxide, under moderate pressure and at a reaction temperature of about 80 C. to about C. If desired, the reaction mixture may subsequently be subjected to neutralization, dehydration and elimination of low boiling materials.

The prepartion of polyloxyalkylene glycol monoalkyl ethers according to the invention for hydraulic brake fluid use is illustrated by the following example:

EXAMPLE 0.8 gram of potassium hydroxide is added to 32 grams of methanol and the mixture is stirred at 60 C. under a nitrogen atmosphere until a clear solution is formed, whereupon this solution is heated to 100 C. To the solution is added 106.5 grams of ethylene oxide (2.42 mols) slowly while maintaining the temperature at 100 C. and the mixture is stirred at that temperature under a pressure of 2 to 4 kg./cm. for 2 hours. Thereafter, 57.3 grams of 1,2-propylene oxide (0.98 mol) is added slowly and reacted under the same conditions. After the reaction is completed, the polymer product is distilled at a reduced pressure of 5 mm. Hg at 65 C. and any low boiling components are thus eliminated. The residue is neutralized by the addition thereto of a 5% by weight sulfuric acid solution and then dehydrated under reduced pressure. To the dried residue, 3% by weight of magnesium silicate absorbent (Allegheny Industrial Chemical Co.) is added and further drying is carried out at reduced pressure and a temperature of 80 C. The absorbent is then separated from the now dry polymer product.

The products produced in the preparation of polyoxy-.

alkylene glycol monoalkyl ethers by this method reflect exactly the mol ratios of the reactants.

In the following table, there is set forth a comparison of polyoxyalkylene glycol monomethyl ethers within the scope of the invention with polyoxyalkylene glycol monomethyl ethers outside the scope of the invention. Samples within the scope of the invention are distinguished from samples outside the scope of the invention by the employing of C as a prefix to designate the samples outside the scope of the invention, i.e., comparative samples. It is noted that according to Japanese Industrial Standard K2233, for hydraulic brake fluids the following are some of the requirements: viscosity at 40 C., less than 1800 centistokes; viscosity at 50 C., greater than 4.2 centistokes; boiling point, greater than C.; and rubber swelling, 0.5 to 5.0%. The corresponding specifications of the Society of Automotive Engineers (U.S.), as referred to in US. Pat. No. 3,062,747, are quite similar, namely: maximum viscosity at -40 F., 1800 contistokes; minimum viscosity at 130 F., 4.0 centistokes; minimum boiling point, 375 F.; and rubber swelling, 4.0% (maximum). Of course, to exceed these requirements, as, for example, by providing a lower viscosity at very low temperatures, is highly desirable.

4 all instances the -mol ratio of alkylene oxide to methanol is at least 4.

The present invention therefore provides unobvious improvements over the prior art, the prior art being represented, for example, by US. Pat. No. 3,062,747 and 3,324,035.

While the invention has been described by reference to Sample 1 -2 0-3 0-4 0-5 0-6 0-7 0-8 0-9 Oxyethylene oxy-l 2- r0 ylene (ratio by weig t) ..P 3 65/35 65/35 65/35 65/35 65/35 65/35 65/35 70/30 70/30 Alkylene oxide/methanol (mol ratio) 3. 4 3. 4 3. 4 3. 4 3. 4 4. 0 4. 0 3. 5 4. 0 Order of addition EO-PO Random EO-PO-EO l PO-EO PO-EO-PO 3 EO-PO EO-PO EO-PO EO-PO Viscosity (centistokes)' 647 1, 013 MWJ 2 MWJ 1, 190 720 1, 120 710 865 C 4. 5 4. 6 4. 8 4. 9 4. 7 4.8 5. 1 4. 7 5. 2 Boiling point (3.).-. 240 241 242 242 241 242 241 239 239 Rubber swelling (percent increase of diameter of rubber cup at 1205:2" 0. after :1:2 hours).. 3. 1 3. 0 3. 1 3. 2 3. 4 3. 0 2. 9 2. 8 2. 6

Sample 0-10 11 0-12 0-13 14 O-l5 C-16 C17 Oxyethylene/oxy-1,2-propylene (ratio by weight) 70/30 /15 85/15 85/15 /10 70/30 85/15 00/10 Alkylene oxide/methanol (mol ratio) 5. 0 3. 5 4. 0 5. 0 3. 5 3. 5 3. 5 3. 5 Order of addition EO-PO EO-PO EO-PO EO-PO EO-PO Random Random Random 780 MWJ MW] 818 MWJ MWJ MWJ 4.8 5.7 7.1 5.1 4.9 5.0 5.3 Boiling point C 238 238 241 242 236 240 239 237 Rubber swelling (percent increase of diameter of rubber cup at =e2 0. after 705:2 hours) 2. 3 0. 4 0. 3 0. 3 0. 7 2. 8 0. 7 0. 6

1 EO-PO-EO molar ratio is 17.565-17.5. 2 MWJ means milky white jelly. 3 IO-EO-PO molar ratio is 25-65-10.

A comparison of viscosities at 40 C. for sample 1 with sample C2 to C5, for sample 8 with sample C-15, for sample 11 with sample C-l6 and for sample 14 with sample C17 clearly shows the importance of following the teachings of the present invention to first react with the methanol the ethylene oxide and then add to the reaction mixture propylene oxide and subsequently not to add any more ethylene oxide, thereby to provide a block copolymer of the above formula in order to obtain particularly low viscosities at very low temperatures. The comparison of sample 1 with samples C-2 to C5 is particularly significant in showing the criticality of first reacting the ethylene oxide with the methanol before adding thereto propylene oxide and subsequently not adding thereto any more ethylene oxide. In US. Pat. No. 3,062,747, the main thrust of the disclosure is to polyoxyalkylene glycol monoalkyl ethers which are hetero copolymers, i.e., which are prepared by reacting the alkanol with a mixture of alkylene oxides. There is brief mention that the reaction of the alkanol with ethylene oxide and 1,2-propylene oxide may be sequential but there is no recognition whatever of the criticality of the sequence being ethylene oxide-propylene oxide as in the present invention rather than propylene oxide-ethylene oxide or ethylene oxide-propylene oxide-ethylene oxide or propylene oxide-ethylene oxide-propylene oxide.

A comparison of the viscosities at -40 C. of sample 1 with samples C-6 and C7, of sample 8 with samples C-9 and C10, and of sample 11 with samples C-12 and C-13 clearly shows the importance for the obtaining of particularly low viscosity at very low temperatures of providing that the alkylene oxide to methanol molar ratio be less than 4.0; it is seen that this becomes particularly important as the oxy-ethylene to oxy-1,2-propylene weight ratio is increased. In contrast to this aspect of the present invention, in U.S. Pat. No. 3,324,035, while among the examples therein are included polyoxyakylene glycol monomethyl ethers in which first ethylene oxide and then 1,2-propylene oxide is added to methanol, in

certain specific embodiments thereof, it is to be understood that the scope of the invention is not to be considered limited by the specific embodiments disclosed but rather is to be determined by the reference to the appended claims.

What we claim is:

1. A hydraulic brake fluid consisting essentially of a poly(oxyethylene-oxy-1,2-propylene) glycol monomethyl ether having an average molecular weight of from about to about 230 and the formula wherein n averages from 1 to 3.7, m averages from 0.3 to 3 and the average total of n and m is from 3.1 to 3.9 and the oxyethylene groups constitute from 65 to 90% by weight of the total weight of oxyalkylene groups present.

2. In a method for applying pressure to a hydraulic brake through a hydraulic brake fluid, the improvement wherein the hydraulic brake fluid consists essentially of a poly(oxyethylene-oxy-1,2-propylene) glycol monomethyl ether having an average molecular weight of from about 160 to about 230 and the formula LEON D. ROSDOL, Primary Examiner D. SILVERSTEIN, Assistant Examiner US. 01. X3. 

